B Cells - Podcast Version TeachMePhysiology 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x B cells (B lymphocytes) are one of three types of lymphocytes in the body (B cells, T cells and natural killer cells). They present antigens to T cells, produce antibodies and are a key component of humoral immunity – part of the adaptive immune response. This article will cover the development, function and life cycle of B cells, including their mature plasma cell and memory B cell forms. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More B Cell Life Cycle B cells develop in the bone marrow before completing maturation in the spleen. They may stay in the spleen or migrate to secondary lymphoid organs, where they become activated upon encountering an antigen. Once activated, B cells undergo the germinal centre reaction, during which they proliferate and are selected with T-helper cell support – before differentiating into antibody-secreting plasma cells or memory B cells. Created in BioRender Fig 1Overview of B cell life cycle B Cell Development B and T cells arise from common lymphoid progenitor cells within the bone marrow. Progenitor cells committed to the T cell lineage migrate to the thymus for maturation, whereas cells committed to the B cell lineage remain in the bone marrow. Developing B cells express a B cell receptor (BCR), which is a membrane-bound immunoglobulin that allows antigen binding. B cells are then selected based on the properties of this receptor – ensuring that it is functional but not strongly self-reactive. This selection process has two components: Positive selection – B cells with a functional BCR receive survival signals and continue development; those without a functional receptor undergo apoptosis. Negative selection – B cells with BCRs that bind strongly to self-antigens undergo receptor editing, functional inactivation (anergy), or apoptosis. This process of selection produces immature B cells, which leave the bone marrow and migrate to the spleen to complete maturation as naïve (antigen-inexperienced) B cells. B Cell Activation Naïve B cells reside in lymphoid (B cell) follicles within the spleen or migrate to other secondary lymphoid organs such as lymph nodes and mucosal-associated lymphoid tissue. This distribution allows immune surveillance of different compartments of the body: B cells in the spleen ‘screen’ for blood-borne antigens B cells in lymph nodes ‘screen’ for antigens in lymph draining from tissues B cells in the various MALTs ‘screen’ for antigens at mucosal surfaces Naïve B cells become activated when they bind a foreign antigen via their BCR. Activated B cells form a germinal centre within the lymphoid follicle they reside in and present their antigen to a T-helper cell. This enables B cells to undergo the germinal centre reaction, during which they proliferate and are selected with T-helper cell support. Following this process, they differentiate into antibody-secreting plasma cells or long-lived memory B cells. Cenveo / CC-BY-3.0-US (http://creativecommons.org/licenses/by/3.0/us/) Fig 2Activated B cells receive help from a T-helper cell and differentiate into plasma or memory cells T-Independent B Cell Activation In most cases, B cells need to interact with T-helper cells for full activation. However, some antigens can activate B cells without T cell help and are termed T-independent antigens. Some examples of T-independent antigens are the lipopolysaccharide (LPS) component of the cell wall of Gram-negative bacteria and the polysaccharide outer layer of encapsulated bacteria. These antigens allow the associated bacteria to evade T cells but can still be recognised by B cells. B cells activated by T-independent antigens mainly produce IgM antibodies and do not generate memory B cells. Plasma Cells Plasma cells are large, terminally differentiated cells with abundant rough endoplasmic reticulum, allowing the production of large quantities of antibodies. They arise following T cell–dependent B cell activation and secrete antibodies either transiently during infection or long term, particularly from the bone marrow. Plasma cells are often found in chronic inflammation. Nephron / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) Fig 3Blood film showing a multinucleated plasma cell Memory B Cells Memory B cells are long-lived cells that remain within the body and allow a more rapid response to future infections as part of a secondary immune response. If the host is re-exposed to the same antigen, these cells rapidly proliferate with assistance from T cells. This produces more cells capable of secreting specific antibodies to the pathogen. As a result, the pathogen is often cleared before infection becomes established or symptomatic. Clinical Relevance X-linked Agammaglobulinemia (XLA) X-linked agammaglobulinemia, also known as Bruton’s disease, is a rare inherited immunodeficiency caused by failure of B cell development in the bone marrow. Affected patients are unable to produce mature B lymphocytes, resulting in markedly reduced or absent circulating immunoglobulins. Symptoms typically become apparent after 6 months of age, when maternally derived IgG has been degraded. Management involves regular immunoglobulin replacement therapy, and some patients require prophylactic antibiotics. Live vaccines are contraindicated, as patients lack functional humoral immunity. Do you think you’re ready? Take the quiz below Pro Feature - Quiz B Cells Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Frequent questions What are B cells and their primary functions in the immune system? B cells, or B lymphocytes, are a type of lymphocyte crucial for humoral immunity. They present antigens to T cells and produce antibodies, playing a vital role in the adaptive immune response. How do B cells develop and mature in the body? B cells originate from common lymphoid progenitor cells in the bone marrow, where they undergo selection to ensure functional B cell receptors. They then migrate to the spleen for maturation before becoming naïve B cells. What triggers the activation of naïve B cells? Naïve B cells become activated upon binding to foreign antigens through their B cell receptors. This activation leads to the formation of a germinal centre, where they proliferate and differentiate into plasma cells or memory B cells. What distinguishes T-independent B cell activation from T-dependent activation? T-independent B cell activation occurs when certain antigens, such as lipopolysaccharides from bacteria, stimulate B cells without T-helper cell assistance. This activation primarily results in the production of IgM antibodies without the formation of memory B cells. What is X-linked agammaglobulinemia (XLA) and its clinical implications? X-linked agammaglobulinemia is a genetic immunodeficiency caused by impaired B cell development, leading to a significant reduction in immunoglobulins. Patients typically require immunoglobulin replacement therapy and are at risk for infections due to a lack of functional humoral immunity. Rate This Article